Michael Hewitt

1996 chevy 1500, so bank 1 sensor 2 and 3 are flat lined at 1070-1080 mV, i unplugged them just to see what happens and they go down to the 430mV range, both new sensors, Im assuming bad ground or the likes where should i start/what color wires am i looking for? thanks, both banks sensor 1's seem to be switching normally, ie ranging from 0-700 mV's ish and fluctuating rapidly.
Mike

tech2

does the truck has 4 02 sensors
pre cat b1s1 and b2s1
post cat b1s2 and b2s2

the pre cat sensors should switch rapidly in closed loop operation, the post cat sensors should not; if the convertors are working properly.

if you unplug a sensor the 450mv you get is a bias voltage from the pcm...this is normal.

i am confused by a sensor 3 that you are reporting? the pre cat sensors are pinned rich?
what type of injection system is used: throttle body or port injection?

Michael Hewitt

the configuration is b1s1 b1s2 b2s1 precat and b1s3 post cat, the headers collect before the cat. the 2 downtstream sensors one pre and one post cat are the ones pinned at 1080mV the b1s1 and b2s1 precat are both seemingly normal to me switching rapidly varying from 0-6 or 700 mV. the injectors are a MPFI conversion that i purchased from ACdelco. all fuel trim does not vary much from 0% except for the b1s2and3 short ter trim is pinned at 99.2%
and thank you for the help!

tech2

don't know what to tell you...I just viewed wiring diagrams for a 5.0L and 5.7L. both show 2 precat and 2 post cat 02 sensors. I viewed a picture of the oem y pipe and it is as you have described.

makes no sense to have 2 precat sensors in the same bank. If it was, it would be switching like the upstream sensor. the data you have provided indicates its switching like a downstream sensor.

does your scan tool read 100%ft as ideal? the adaptive adjustment limit for fuel trim is 30%....no way it can reach a 99% adjustment correction. At 30% it would be setting a dtc. Are you getting lean or rich dtc?

Michael Hewitt

so the higher mV on the sensors is when they are plugged in and the lower is when they are disconnected.
there are 2 downstream sensors one is before CAT and other is after.

Michael Hewitt